In very general terms, the art of printing involves application of an opaque medium, often in a liquid or semi-liquid ink form, to a background material such as paper. The ink marks on the paper or other medium typically take the form of language characters (letters) and graphics (pictures).
Historically, and particularly before the relatively recent advent of computerized systems, printing has been accomplished on apparatus known generally as printing presses.
Most printing presses have some common features. For example, in most printing presses, raised type is used, ink is applied to the type faces in liquid or paste form, such as by rollers, and the actual printing is accomplished by bringing the inked typefaces into contact with the medium, such as paper. The ink is transferred in the process from the typefaces to the paper or other medium.
There have been developed over the years many types of printing presses. Some print on single sheets, rapidly and successively fed, and others use type set on rollers to print on continuous webs of paper. Newspapers have been typically printed by this technique.
Another common and well-known printing machine that has been around a long while is the typewriter. In typewriters, individual type heads are moved to strike an inked ribbon in near proximity to the paper or other medium upon which printing is desired. As each letter is printed, a mechanism moves the strike region to the next character space to be printed. Many ingenious mechanisms have been developed for typewriting.
With the advent of computers, many new developments have been made in printers. Typesetting for high-volume printing machines is now computerized. In the area of general-purpose personal computers, printers operated by such computers have become as common in modern offices as typewriters were in offices of times past.
There are a variety of types of printers used with personal computers. Some are similar in form to typewriters, such as dot matrix printers, which use a mechanism to strike a ribbon to transfer ink to paper. Others, known in the industry as ink-jet printers, spray ink from multiple tiny nozzles to provide characters and graphics on paper. Still others, called laser printers, use a laser to write characters and graphics on a drum, which then attracts ink in a fine powder form, which is transferred to paper and fused by heat to the paper. Laser printers have enjoyed enormous success.
A very common requirement in printing is making multiple copies. Forms like shipping labels, for example, often must be made in multiples, so different people responsible in a phase of the operation of transport may each have an exact copy of the original. Exact copies are reliably provided by carbon sheets between layers of paper, and by later print-through types of forms that mimic the familiar carbon-copy operation without the need for intermediate sheets.
There is a serious limitation, however, to the common print-through copy-making technique. The technique is severely limited to impact-type and pressure type printers, because the print-through requires pressure in the shape and form of the characters and graphics to be printed. Printers like ink jet and laser printers, that do not employ pressure devices, can't use the technique, and the only way to make multiple copies with these printers is by repetition. Repetition is slow and costly.
What is clearly needed is a way usable by all kinds of printers that apply ink to paper to make multiple copies in a single pass.